The invention relates to improvements in combination locks of the type known as permutation locks. More particularly, the invention relates to improvements in combination locks of the type wherein two or more tumblers can be rotated and/or otherwise moved to predetermined positions in order to establish the conditions for retraction of a locking hasp or bolt from an extended or operative position to an inoperative or retracted position.
It is already known to provide a combination lock with a set of rotary tumblers which are movable by a rotary knob to and from predetermined angular positions in which a dog of a pivotable link or lever is free to enter peripheral notches of all tumblers and in which a pallet or tooth of the link can enter a cam on the shaft of the knob. Reference may be had to commonly owned German Pat. No. 30 29 735 to Morold. The complexity of manipulations which must be carried out prior to establishment of conditions for retraction of the locking bolt depends upon the number of tumblers and on the complexity of selected combination or code which must be followed in order to move each tumbler to a predetermined position in which the notches of all tumblers are ready to receive the aforementioned dog. The knob which is used to turn the tumblers must be rotated by hand. When the notch-aligning operation is completed and the pallet of the link has entered the recess of the cam, the knob is rotated by hand in order to retract the locking bolt from the extended position. The means for simplifying the task of the operator who is in charge of turning the knob in a clockwise and/or counter-clockwise direction between a number of different angular positions in order to align the notches of all tumblers and to align the recess of the cam with the pallet of the link normally includes a scale which carries a large number of graduations (e.g., graduations numbered from zero to ninety nine). For example, and if the combination lock comprises four rotary tumblers, it is necessary to turn the knob five times in a clockwise direction to select the first digit of a four-digit combination, thereupon four times in a counterclockwise direction to select the second digit of the combination, thereupon three times in a clockwise direction to select the third digit of the combination, and finally twice in a counterclockwise direction to select the fourth digit of the combination. The next step involves clockwise rotation of the knob in order to retract the locking bolt from the extended or operative position.
The carrying out of a total of, for example, fifteen successive angular movements consumes much time. In addition, each turning step must be carried out with utmost care, i.e., the operator must observe the graduated scale in order to ensure that the knob is actually moved to a given position of register with a particular graduation on the scale. Still further, the operator must memorize the sequence and the extent of angular movements of the knob in clockwise and counterclockwise directions, or the operator must continuously refer to a piece of paper or other carrier of information denoting the selected combination. A single minor error (e.g., improper selection of only one of a large number of different angular positions of the knob or rotation of the knob in the wrong direction) renders it necessary to repeat the entire operation with attendant losses in time. It has been found that, as a rule, each successful attempt to open a combination lock with, for example, four tumblers is preceded by at least one unsuccessful attempt and quite often by a series of several successive unsuccessful attempts.
Nevertheless, combination locks which employ a plurality of tumblers are gaining in popularity because they can effectively prevent (or render very difficult) unauthorized opening of doors on vaults, safes and other structures. Moreover, a combination lock can be opened without resorting to a key.